The present invention is directed to formaldehyde-free binders for use in the formation of nonwoven products to be utilized in areas where heat resistance is important. Such products find use in a variety of applications including in roofing, flooring and filtering materials.
Specifically, in the formation of asphalt-like roofing membranes or the like, such as those used on flat roofs, polyester webs or mats about one meter in width are formed, saturated with binder, dried and cured to provide dimensional stability and integrity to the webs allowing them to be used on site or rolled and transported to a converting operation where one or both sides of the webs are coated with molten asphalt. The binder utilized in these webs plays a number of important roles in this regard. If the binder composition does not have adequate heat resistance, the polyester web will shrink when coated at temperatures of 150.degree.-250.degree. C. with the asphalt. A heat resistant binder is also needed for application of the roofing when molten asphalt is again used to form the seams and, later, to prevent the roofing from shrinking when exposed to elevated temperatures over extended periods of time. Such shrinking would result in gaps or exposed areas at the seams where the roofing sheets are joined as well as at the perimeter of the roof.
Since the binders used in these structures are present in substantial amounts, i.e., on the order of about 25% by weight, the physical properties thereof must be taken into account when formulating for improved heat resistance. Thus, the binder must be stiff enough to withstand the elevated temperatures but must also be flexible at room temperature so that the mat may be rolled or wound without cracking or creating other weaknesses which could lead to leaks during and after impregnation with asphalt.
Binders for use on such nonwoven products have conventionally been prepared from acrylate or styrene/acrylate copolymers containing N-methylol functionality. In this case, the curing of the emulsion polymer is effected via crosslinking with the methylol groups and subsequent release of formaldehyde. Because of the inherent problems of the toxicity and potential health effects encountered during exposure to even small amounts of formaldehyde, there exists a real need for alternatives to formaldehyde-based crosslinking systems.